1. Field of the Invention
This invention generally relates to a semiconductor memory device, and, in particular, to controlling multiple signal polarity in a semiconductor device based upon the particular usage of the semiconductor device.
2. Description of the Related Art
Modem integrated circuit devices are comprised of millions of semiconductor devices, e.g., transistors, formed above a semiconductor substrate, such as silicon. These devices are very densely packed, i.e., there is little space between them. Similarly densely packed electrically conducting lines may also be formed in the semiconductor substrate. By forming selected electrical connections between selected semiconductor devices and selected conducting lines, circuits capable of performing complex functions may be created. For example, bits of data may be stored by providing electrical current to a plurality of bit lines and an orthogonal plurality of word lines that may be electrically coupled to one or more capacitors in a semiconductor memory.
The semiconductor memory may be a dynamic random access memory, a flash memory, and the like. The semiconductor memory typically comprises an array of memory cells, address decoding circuitry for selecting one, or a group, of the memory cells for reading or writing data, sensing circuitry for detecting the digital state of the selected memory cell or memory cells, and input/output lines to receive the sensed data and convey that information for eventual output from the semiconductor memory. In many cases, the array of memory cells will be sub-divided into several sub-arrays, or subsets, of the complete collection of memory cells. For example, a semiconductor memory having 16 megabits (224 bits) of storage capacity may be divided into 64 sub-arrays, each having 256 K (218) memory cells.
Typically, the semiconductor memory has a plurality of signal pads for enabling or disabling certain electronic functions by providing signals on these signal pads. For example, a memory device may include a clock enable (CKE) signal pad and a data mask (DM) signal pad, among the various other signal pads that may be used by the memory for a variety of other functions. Typically, the CKE signal pad is used to generate a clock enable signal to implement a power-down or self-refresh mode of the memory; whereas, the DM signal pad is utilized to mask or unmask data stored within the memory. Usually, the CKE and DM signal pads are preconfigured by the manufacturer to be disposed in a particular state by default (i.e., these signal pads are usually put in a default active high state). If the user desires to enable a power down mode, for example, the CKE signal pad needs to be driven from the default active high state to a low state (i.e., pulled down low from Vcc) to perform the power saving function. Similarly, if the user does not desire to mask data, for example, the DM signal pad must also be driven from the default active high state to a low state to disable the data masking function of the memory device. Often, some signals have to be driven to an opposite state, as opposed to its default active state, for certain applications. In other words, some applications of devices, such as memory devices, may require active high signals to be pulled low for a substantial amount of time.
By changing the states of these signal pads (i.e., from a high state to a low state) typically requires more current to do so, and, consequently, increases the power drain on the memory when a memory device has on-die termination. When the memory device has on-die termination to Vcc, there may be a current draw when driving the a signal pad to a logic low state. Conversely, when the memory device has an on-die termination to Vss, there may be a current draw when driving a pin to a logic high state. Therefore, more current is drawn when the signal pad is pulled down from Vcc to ground on an on-die termination to Vcc (or when the pad is pulled high from Vss on a on-die termination to Vss) to enable the function of the signal pad. This becomes even more problematic when the memory is implemented in a portable configuration (e.g., a portable computer) with a limited supply of power. For example, if the user does not desire to mask data the majority of the time, then more current drain typically results (and, thus a larger power drain) in order to drive the DM signal pad from its default active high state to the desired active low state such that data that is stored within the memory would not be masked.
The present invention is directed to overcoming, or at least reducing, the effects of, one or more of the problems set forth above.